1. Field of the Invention
The present invention relates to a method and apparatus for measuring the velocity in a two-dimensional field of view of a fluid in a flow field by processing television picture information of a flow field visualized by the tracer particle injection method.
2. Description of the Prior Art
For detecting the velocity distribution of a flow field of, for example, a fluid such as water in a duct, it is well-known to visualize the flow field by injecting particles of nylon or the like into the flow field as tracers. For obtaining velocity information on a flow field visualized in this manner, there has been proposed a method for measuring flow field velocity comprising the steps of obtaining a television video signal corresponding to the condition of the visualized flow field by means of a television camera, making two frame signals from the two field signal components composing a frame of the television picture, subjecting particle pathline images in pictorial images corresponding to the frame signals to a thinning process, deriving the correspondence between the particle pathline images of the two pictorial images from the angle of inclination and the length of the thin lines obtained, and determinating the velocity in the flow field from the difference in location between the two pathline images formed by one and the same particle (Journal of the Flow Visualization Society of Japan, Vol. 9, No. 34, Pages 379 to 382). Since the proposed method needs only one television picture frame, it is more widely applicable than one which needs two or more frames.
The proposed method includes a step of obtaining the angle of inclination and the length of each skeleton line obtained by subjecting the particle pathline images to the thinning operation and a tracking step for determining the pathline of the fluid in the flow field. Therefore, the proposed method has the disadvantage that the result of the tracking operation is markedly affected by any noise superposed on the pictorial image, whereby erroneous velocity is apt to arise in the result of the measurement.
For obtaining reliable result in this case, it is necessary to establish an excellent lighting condition for visualizing the flow field, and moreover, to use tracer particles of a diameter falling within a predetermined range. This latter need results from the fact that the lengths of the thin lines obtained by subjecting the particle pathline images to thinning vary with the diameter of the tracer particles even if their pathline images are identical in length. Accordingly, it is necessary for realizing the proposed method to overcome the problems described above.
Theoretically, it is possible to use Hough transformation for obtaining the angle of inclination and the length of the particle pathline images. In fact, however, it is difficult to use Hough transformation because an impractically long processing time is needed. Furthermore, it may be difficult to obtain a reliable measurement result due to the effect of the noise contained in the pictorial image being processed.